This invention relates broadly to hub constructions which mount and automatically center discs and the like for driving rotation, and more particularly to self-centering hubs for use with thin, pliant or flexible discs, particularly the rather fragile such discs which carry magnetic recording media on their surfaces and are used as magnetic records, especially in the recording of bit-form digital data.
Data recording apparatus using pliant or flexible magnetic recording discs have come into increasingly frequent use in relatively recent times, largely because of the inherent advantages of disc recording (basically, very short access time and relatively large storage per unit), coupled with the relative inexpensiveness, and ease of using, modern flexible discs and disc files, for example of the type shown in U.S. Pat. No. 3,668,658.
In using such flexible discs, the concentric data tracks are exceedingly narrow and closely-spaced; thus, it is extremely important that the disc be accurately centered each time it is used, since radial errors even on the order of less than 5 mils are usually unacceptable and will preclude successful tracking to retrieve the recorded data. Furthermore, the recording discs are, as stated, flexible in nature (often being referred to as "floppy" discs) and somewhat fragile, being typically a mere sheet of plastic film such as Mylar on the order of about 3 to 4 mils thick, including the magnetic coating, and are thus easily stretchable, particularly at their centers, where the discs have a simple aperture for direct mounting upon a drive hub. In the past, mounting of the discs was accomplished mainly by use of a tapered hub which tended to center the disc as the latter was moved along a diverging tapered section into position against a flat, annular clamping surface. As a result of the requisite accuracy in centering the disc for proper recording or replay, however, the extreme accuracy required in properly machining such a tapered hub made the same basically impractical, as did the fact that the central hubs are subject to deformation and enlargement during the numerous times they are mounted and dismounted during their useful life. Also, the discs must, in order to be truly practical, be useful on different individual recorders, as well as on recorders made by different manufactureres, all of which are subject to dimensional variance even under the best of conditions.